1. Field of the Invention
The invention relates to automatic swimming pool cover systems, and in particular to the cover drum around which a pool cover with beaded side edges winds and unwinds as it retracts and extends across a swimming pool.
2. Description of the Prior Art
Automatic swimming pool cover systems typically include a flexible vinyl fabric sized so that most of it floats on the surface of the pool water. The pool water acts as a low friction surface significantly reducing the amount of force required to move the cover across the pool. The front edge of the cover is secured to a rigid boom spanning the width of the pool for holding the front edge of the cover above the water as it is drawn back and forth across the pool.
To draw the cover across the pool, a cable, typically a Dacron line, is incorporated into and forms a beaded tape which is sewn or attached to the side edges of the pool cover. The beaded tape in turn is captured and slides within a "C" channel of an extruded aluminum track. The track is secured either to the pool deck or the the underside of an overhanging coping along the sides of the swimming pool. The cables extending from the beaded tape sections of the cover are trained around pulleys at the distal ends of the tracks and return in a parallel "C" channel to a drive mechanism where they wind onto cable take-up reels.
To uncover the pool, the drive mechanism rotatably drives a cover drum mounted at one end of the pool winding the pool cover around its periphery unwinding the cables from the take-up reels. To cover the pool the drive mechanism rotatably drives the cable take-up reels winding up the cables to pull the cover across the pool unwinding the cover from the cover drum.
Typically, the cover drum has a length shorter than the width of the pool cover so that the thicker beaded edges of the cover overhang the ends of the drum. This is because the beaded edges of the cover are somewhat thicker than the main body of the cover, and if they were wound around the periphery of the cover drum, the cover winding around the drum would increase in circumference more rapidly at its edges than at its center and therefore, would tend to wind more rapidly than the central body of the cover.
Also to assure that the central section of the cover winds tightly about the periphery of the cover drum, the cover drum may be canted slightly with respect to the cover such that the cover helically winds about the cover drum in a fashion that prevents overlapping of the beaded cover edges. [See U.S. Pat. No. 4,060,860, Lamb, FIGS. 6 and 7.] However, canting of the cover drum for helically winding the cover about its periphery means that the beaded edges of the cover must be allowed to translate relative to the track channels securing the edges of the cover along the sides of the pool, i.e., the cover edges are not aligned with and must be guided into the track channels as the cover winds and unwinds from around the cover drum. [See U.S. Pat. No. 3,050,743, Lamb.]
Also, the rate at which the pool cover unwinds from and winds onto the cover drum depends on the diameter of the roll of the cover still wound around the drum, i.e., the rate is greatest when most of the cover is wound around the drum (largest diameter) and least when the cover is practically unwound from the drum (least diameter). The same phenomenon occurs as the cables wind onto and unwind from the cable reels. It should be appreciated that the cables wind onto the cable reels at the highest rate when the cover unwinds from the cover drum at its lowest rate and visa-versa.
In systems where the cable take-up reels and the cover drum rotate together on the same shaft, but oppositely wind/unwind the cables and cover respectively, a spring is utilized as a tensioning take-up mechanism to compensate for the different and varying rates at which the cables and pool cover wind and unwind from the respective reels and drum during the opening and closing cycles. The spring mechanism lengthens and shortens the cable path as the cover is drawn back and forth across the pool taking up and yielding slack in the respective cables as necessary to compensate for the difference in the winding and unwinding rates of the reels and drum. [See U.S. Pat. Nos. 3,747,132 and 3,982,286, Foster.]
In spring tensioning take-up systems of the type described by Foster, and later floating spring tensioning take-up systems of the type pioneered by Last, the applicant herein, the tensioning of the cables by the spring(s) assures that the cover, and especially its beaded edges curling around the ends of the drum, wind tightly and uniformly without substantial bias around the cover drum as the cover is retracted from across the pool. [See U.S. Pat. No. 3,982,286, Foster, Col. 5, 1.36-Col. 6, 1.4. See also co-pending application Ser. No. 07/258,000, now U.S. Pat. No. 4,939,798.]
In other systems a clutching mechanism is typically utilized to decouple the rotation of the cable reels from that of the cover drum as it is rotatably driven to wind the cover onto the drum uncovering the pool, and to decouple the rotation of the cover drum from that of the cable reels as they are rotatably driven to draw the cover across the pool. Typically, in such systems, the cable reels are allowed to free wheel when the cover drum is rotatably driven and conversely, the cover drum to free wheel when the cable reels are rotatably driven. [See U.S. Pat. Nos. 3,019,450 and 3,050,743, Lamb.]
In such clutch decoupled systems of the type pioneered by Lamb, in order to prevent biasing of the cover as it winds around the cover drum during retraction and to assure that the cover winds compactly and uniformly around the drum, adjustable braking mechanisms are utilized to slow or resist rotation of the respective free wheeling take-up reels to provide the necessary tension in the cables for assuring that cover edges curl around the ends of the cover drum. Such braking mechanisms typically are adjustable for each take-up reel.
In early automatic pool cover systems the rigid boom spanning the width of the pool holding the front edge of the cover above the water was typically supported by a pair of wheeled dollies rolling on the side edges of the pool. The cables moving within the "C" channels of the track along either side of the pool were either directly secured in some fashion to the rigid boom, [Foster, supra], or were indirectly secured to the ends of the boom via fabric interfaces referred to as gores. [See U.S. Pat. No. 4,001,900, Lamb].
Slider mechanisms have now supplanted the use of wheeled dollies for supporting the rigid boom carrying the front edge of the cover. Typically, such slider mechanisms are coupled to the respective ends of the boom and have an edge adapted for capture and sliding within the same or different "C" channels of the extruded track in which the beaded side edge of the cover is captured and slides. [See U.S. Pat. No. 4,686,717, MacDonald et al and U.K. Pat. No. 2,072,006, Lee.]
As pointed out and extensively discussed in co-pending application Ser No. 07/258,000 filed by the Applicant, now U.S. Pat. No. 4,939,798, in systems where slider mechanisms support the rigid boom, it is very important to maintain the boom oriented squarely between the track channels, otherwise the sliders carrying the boom will jam in the track channels stopping extension or retraction of the cover. Even with wheel supported booms, any canting during extension or retraction will tend to pull the beaded cover edge free of the confining track channels particularly at its front corners.